It is known that engine performance deteriorates when sediment such as sludge is formed inside the engine. Therefore, the inhibition of the sediment formation has been attempted by adding various types of additives to a fuel or a lubricant.
For example, Patent Document 1 discloses a diesel engine lubricant additive consisting of oxycarboxylic acids capable of dispersing water-containing calcium sulfate in oil. Such additive is capable of dispersing calcium sulfate, which is a component of sludge, in a lubricant and is capable of decreasing sludge sedimentation. Also, an apparatus or a composition used for cleaning an engine combustion chamber has been known (for example, Patent Documents 2 and 3).